Respiratory Acidosis in COPD
Heide Thorne RN BSN
March, 2012
MSN 621
Mr. G presents to the emergency room:
Mr. G is a 64 year old, barrel-chested
man who smokes 1 pack of cigarettes
a day. He is short of breath and
tachypneic with a productive cough.
He is using home oxygen at 2 liters per
nasal cannula. He recently ran out of
his bronchodilators. He has a history
of COPD. His O2 saturations are 88%
on room air.
The learner will know:
• Causes of COPD.
• What compensatory mechanisms look like in Chronic
COPD.
• Why oxygenating the CO2 retainer is done cautiously.
• Preventative measures to advise the patient with
COPD.
Causes:
• Progressive, recurrent airflow obstruction of
pulmonary airways causing decreased O2 intake & CO2
retention.
• Repeated inflammatory response to noxious
gases/particles (smoking indicated in 90% of cases).
• Host and environmental factors exist (i.e. chronic
bronchitis, emphysema and 2nd hand smoke).
• Hereditary cause: α1 -antitrypsin deficiency.
(Learning about alph-1 antitrypsin deficiency (AATD), 2012)
(Porth, 2009)
This flow chart illustrates how the disease process of Emphysema
relates to smoking and 𝛼1 -antitrypsin deficiency. 𝛼1 -antitrypsin
is a protein that protects the lungs. (Porth & Matfin, 2007)
smoking
Attraction of
inflammatory cells
Release of elastase
Action inhibited by
𝛼1 -antitrypsin
Decreased 𝛼1 -antitrypsin
activity
Inherited 𝛼1 -antitrypsin
deficiency
Destruction of elastic
Fibers in lung
EMPHYSEMA
A Die Hard Habit
• Smoking is the leading cause of COPD.
Exposure to nicotine causes
inflammation & decreased elasticity
of lungs.
• PaCO2 depends on CO2 production &
alveolar ventilation. Smoking causes a
decrease in alveolar function which
leads to hypercapnia. O2 intake is
decreased and CO2 is unable to be
exhaled.
• Mechanical inefficiency of the respiratory system is due in part to
decreased elasticity of lungs and demands accessory muscle use and
hyperinflation of lungs; another factor in hypercapnia (this is the
cause of a barrel chest).
(Quinn & Sinert)
http://www.pharmacy-and-drugs.com/illnessessimages/copd.jpg
A “2 for 1“ Disease
• Name two types of obstructive airway disease
that when chronic, play a role in COPD?
(Porth & Matfin, 2009)
Chronic Bronchitis
Emphysema
That’s correct! Increased mucous production
& chronic productive cough means
obstruction of small airways.
Bingo! This leads to enlargement of
airspaces & destruction of lung tissue.
Pneumonia
Let’s think this through. Pneumonia can be a
complication of COPD but does not
contribute to the actual cause.
Which way did he go?
ABG’s are drawn on Mr. G.
pH=7.28
PaCO2=60
What respiratory state is he in and which lab value
dictates your decision?
Acidosis; dictated by
pH & CO2
Yes! Respiratory Acidosis exists when the pH
is <7.35 & CO2 is >50. Both values matter
when diagnosing Respiratory Acidosis.
Acidosis; dictated
by pH only
Alkalosis; dictated
by CO2 only
Partly correct. Acidosis exists when pH is
<7.35. CO2 values differentiate between
Respiratory & Metabolic acidosis . You will
need to know this to treat Mr. G correctly.
Let’s rethink this. Alkalosis exists when the
pH is >7.45. CO2 levels can be altered in
Respiratory & Metabolic states so it won’t
help you by itself.
Treatment
An inflammatory response to bacterial & chemical
toxins can exacerbate COPD. Consider why these
medications might be used to decrease the
inflammatory response in the lungs? Click on each box
to check your knowledge.
Bronchodilators
These will relax smooth muscle in the lungs
& improve lung emptying. Ie. Albuterol &
Atrovent
Antibiotics
Antibiotics may be helpful when a bacterial
infection is suspected.
Glucocorticoids
Advair & Pulmacort are common inhaled
steroids used to regulate the inflammatory
response in the lungs.
What’s normal?
http://faculty.ucc.edu/biology-atsma/misc/resp102.htm
http://humanisamiracle.imanisiteler.com/6_clip_image018.jpg
Compensatory Mechanics
We know those with COPD will typically have less O2
intake because of restrictive airways and retain CO2 due
to ineffective gas exchange in the alveoli.
Chemoreceptors adjust to this new “normal” elevated
CO2 and a normal pH is achieved despite a hypoxic
state.
Renal compensation involves the conservation of HCO3
after prolonged hypercarbia due to decreased alveolar
ventilation. This will also help Mr. G’s pH to reach a
normal level.
(Mosenifar MD, 2011)
To oxygenate or not to oxygenatethat is the question.
Compensatory mechanisms may take 1-3 days to achieve Mr. G’s
new “normal” pH. Patients with chronic hypercapnia no longer
sense the need to increase ventilations because of the
decreased sensitivity of the central chemoreceptors. Peripheral
chemoreceptors begin to “kick in” when the PO2 <60mm Hg.
Therefore, if oxygen administration increases Mr. G’s PO2 level
beyond his new “normal,” then his ventilatory drive may be
depressed. Similarly, it is the withdrawal of the oxygen after the
exacerbation that must be a gradual process so as to avoid
sudden shifts in pH. A person who is dyspneic & hypoxic should
be given enough oxygen to meet their metabolic needs.
(Inspired Technologies, Inc, 2007)
(Porth, 2009)
Mr. G’s “normal”
pH changes stimulate chemoreceptors that will change
breathing rate & depth. COPD exacerbation induces
Respiratory Acidosis initially and Mr. G’s pH will be
_____. He will attempt to adjust his pH by “blowing
off” _____. With chronic obstructive problems, O2
cannot reach alveoli (where O2 & CO2 are exchanged),
causing Mr. G to grow accustomed to CO2 retention.
Renal compensatory mechanisms will attempt to
normalize Mr. G’s pH in his chronic respiratory acidotic
state.
Decreased; CO2
Yes! A low pH = acidosis.. Exhaling CO2 is
the mechanism to raise pH!
Unchanged; steam
Increased; HCO3
Lets think about this. His chemoreceptors
have already been stimulated by a change in
pH. CO2 is exhaled & H2O is retained.
Nice try, but an increased pH.=Alkylosis.
HCO3 is retained in the kidneys as an
attempt to raise the pH.
Oxygenation
Why are current guidelines for oxygen therapy to
maintain O2 saturations between 90-92% and not
above 95%?
(Global Initiative for Chronic Obstructive Lung Disease, Inc, 2011)
Patients with COPD will never reach 95%.
This is not true. If administering 100%
oxygen by a mask, it is often possible to get
this patient above 95%, but it isn’t the best
practice.
A normal pH associated with a low PO2 but
an elevated CO2 is typical of chronic
hypercapnia.
This is true. Compensation in respiratory
acidosis can take place & patients become
chronic CO2 retainers. However, adequate
oxygenation should be a a primary concern.
Mr. G will become oxygen dependent for life
if we keep his saturations at 95%.
Oxygenating him won’t cause O2
dependency, however, Mr. G has developed
a new “normal.” High flow oxygen can cause
a paradoxical exacerbation in the patient
who has developed compensatory
mechanisms.
An Ounce of Prevention
After recovery, the FNP encourages Mr. G to get the flu
& pneumonia vaccines. Why is this an important
preventative measure for Mr. G?
Lung infections cause an inflammatory
response, thereby creating more mucous &
air flow resistance.
Exactly right!
Vaccines can prevent COPD.
It is required by law
This isn’t true.
That would be nice but vaccines can only
build the immune response to infections that
will exacerbate COPD. Several bacterial lung
infections can be prevented by the
pneumococcal vaccines.(Hunter & King,
2001)
You should know…
• Hypercapnia as a normal state in the patient with
COPD exacerbation. (slide 12)
• Common treatments of COPD. (slide 10)
• Careful considerations when oxygenating a
patient with COPD. (slide 13)
• Strategies to prevent COPD exacerbations. (slide 16)
Literature Cited
(n.d.). Retrieved March 5, 2012, from All About Pharmacy and Drugs: http://www.pharmacy-and-drugs.com/illnessessimages/copd.jpg
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http://pathlabmed.typepad.com/surgical_pathology_and_la/2009/12/pink-puffer-versus-blue-bloater.html
Diwan, P. (2007, November 16). Retrieved March 5, 2012, from TopNews: http://www.topnews.in/files/healthy-vs-copd.jpg
genome.gov. (2012, January 4). Learning about alpha-1 antytripsin deficiency (AATD). Retrieved February 12, 2012, from National Human
Genome Research Institute: http://www.genome.gov/19518992
Global Initiative for Chronic Obstructive Lung Disease, Inc. (2011). Global Initiative for Chronic Obstructive Lung Disease. Retrieved February
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Mosenifar MD, Z. (2011, October 10). Chronic obstructive pulmonary disease workup. Retrieved March 17, 2012, from WebMD:
http://emedicine.medscape.com/article/297664-workup#aw2aab6b5b2
Porth, C. &. Matfin, G. (2009). Pathophysiology: Concepts of altered health. Philadelphia: Lippincott, Williams & Wilkins.
Quinn, A. D., & Sinert, R. (2009 November 13). emedicine. (E. M. Schraga, Ed.) Metabolic acidosis in emergency medicine. Retrieved February
24, 2012, from Medscape: http://emedicine.medscape.com/article/768268-overview#a0104